Under these agreements, the libraries select books from their collections to submit to Google for inclusion in the project. Google makes a digital scan of each book, extracts a machine-readable text, and creates an index of the machine-readable text of each book. Since 2004, Google has scanned, rendered machine-readable, and indexed more than 20 million books, including both copyrighted works and works in the public domain. The vast majority of the books are non-fiction, and most are out of print. The digital corpus created by the scanning of these millions of books enables the Google Books search engine. Members of the public who access the Google Books website can enter search words or terms of their own choice, receiving in response a list of all books in the database in which those terms appear, as well as the number of times the term appears in each book. The court stated: "The search tool permits a researcher to identify those books, out of millions, that do, as well as those that do not, use the terms selected by the researcher. Google notes that this identifying information instantaneously supplied would otherwise not be obtainable in lifetimes of searching." The search engine also makes possible new forms of research, known as "text mining" and "data mining." Google's "ngrams" research tool draws on the Google Library Project corpus to furnish statistical information to Internet users about the frequency of word and phrase usage over centuries. This tool permits users to discern fluctuations of interest in a particular subject over time and space by showing increases and decreases in the frequency of reference and usage in different periods and different linguistic regions. It also allows researchers to comb over the tens of millions of books Google has scanned in order to examine "word frequencies, syntactic patterns, and thematic markers" and to derive information on how nomenclature, linguistic usage, and literary style have changed over time. The court concluded as to the search function: "We have no difficulty concluding that Google's making of a digital copy of Plaintiffs' books for the purpose of enabling a search for identification of books containing a term of interest to the searcher involves a highly transformative purpose, in the sense intended by Campbell." Downloading and storing complete digital copies of entire books was such copying as "was essential to permit searchers to identify and locate the books in which words